In contrast, bitcoind provides a facility to import a private key without creating a sweep transaction. This is considered very dangerous, and not intended to be used even by power users or experts except in very specific cases. Bitcoins can be easily stolen at any time, from a wallet which has imported an untrusted or otherwise insecure private key - this can include private keys generated offline and never seen by someone else.

Why is this dangerous? Can somebody clarify? How is this different from inporting keys in a bitcoin-QT wallet?

Whomever wrote that paragraph wasn't thinking very much about what they were saying. It's ambiguous and confusing.

Relying on importing a private key to load funds into a wallet can be risky if the person that imports the private key isn't the person that generated it, or if the person that imports the key didn't generate it in a secure manner. This isn't unique to boitcoind. It's true of any wallet that allows you to directly import private keys.

Perhaps it can be phrased better. The important thing is that it conveys that importing private keys is dangerous and shouldn't be done.

So please make it better. And do what do you mean by "dangerous"? Privacy problem? There is no problem in importing a private key unless it is generated by another person or made in a non-secure way. So if it is privacy problem, then please correct that too.